Induction of stilbene synthase and cinnamyl alcohol dehydrogenase mRNAs in Scots pine (Pinus sylvestris L.) seedlings

Pine is known to respond to ozone by the induction of stilbene synthase (STS) and cinnamyl alcohol dehydrogenase (CAD) activities. Here we describe the influence of ozone on STS and CAD transcript levels, as well as on the amounts of actin mRNA and chlorophyll a/b-binding protein (cab) mRNA in needles of young Scots pine (Pinus sylvestris is L.) seedlings. A single ozone pulse of 0.3 mu L.L-1 for 8 h resulted in transient increases in STS, and CAD mRNA levels. In contrast, actin and cab transcript levels were reduced. Treatment of Scots pine seedlings with ozone (0.3 mu L.L-1, 8 h.d(-1)) over a period of 12.5 d resulted in a constant high CAD mRNA level. In contrast STS transcripts were transiently induced over 6 d under these conditions. These results indicate selective ozone responses by the two genes. Compared with results for ozone fumigation alone, combined ozone/UV-B treatment led to a slightly higher increase in STS mRNA in primary needles, as well as in cotyledons. This points to an additive effect by the two stressors. In-situ hybridization with STS and CAD antisense mRNAs revealed an enhanced uniform labeling of mesophyll cells in tissue cross-sections of ozone-treated needles, whereas in the epidermal cell layer the amount of silver grains was unaltered in comparison with controls.